1. Technical Field of the Invention
The present invention relates to an improvement in an electric connecting terminal, wherein tips of at least one pair of piercing portions erected on both side edges of a plane portion of the electric connecting terminal penetrate through a coating and a conductor in a flat circuit body and then the tips is fold in such a direction as to approach each other, thereby connecting the electric connecting terminal to the flat circuit body.
2. Related Art
FIG. 14 shows a flat circuit body 1 and a related electric connecting terminal 2 to be connected to the flat circuit body 1.
The flat circuit body 1 is an FFC (flexible flat cable) which is finished to be a band-shaped cable having a flexibility as a whole by coating a plurality of elongated thin-plate shaped conductors 4a, 4b, . . . with a thin film-shaped insulating coating 5. The conductors 4a, 4b, . . . are formed by various manufacturing methods, for example, are formed by pattern printing or by sticking a preformed tape-like conductive material onto an insulating sheet.
The electric connecting terminal 2 is disclosed in JP-A-11-144780, for example, and has such a structure that a plane portion 6, a plurality of pairs of piercing portions 7 and 8 erected on opposite side edges at the base side of the plane portion 6 and a terminal connecting portion which is formed on the tip side of the plane portion 6 and is not shown are integrally provided.
The terminal connecting portion (not shown) is to be connected to another connecting terminal and, for example, is formed to have a female terminal structure to be accommodated and held in a connector housing or a male terminal structure.
The piercing portions 7 and 8 are provided with taper portions 7a and 8a having a width gradually reduced from a base portion toward a tip and an almost triangular shape seen from the side such that the flat circuit body 1 can be easily pierced and penetrated. Taper surfaces 7b and 8b for gradually reducing a plate thickness toward a tip are also provided on the external surface side of a tip portion.
The electric connecting terminal 2 is a so-called piercing terminal, and the tips of the piercing portions 7 and 8 provided on opposite side edges of the plane portion 6 penetrate through the coating 5 and the conductor 4a (4b) in the flat circuit body 1 by using a caulking device 9 and are then folded in such a direction as to approach each other as shown in FIGS. 15 and 16. As shown in FIG. 17, consequently, the electric connecting terminal 2 is connected to the flat circuit body 1 electrically and mechanically.
More specifically, the conductor 4a (4b) of the flat circuit body 1 can be connected to the electric connecting terminal 2 by causing each of the tips of the piercing portions 7 and 8 to penetrate through the flat circuit body 1 and folding the tip without peeling the flat circuit body 1. Consequently, the number of the processing steps required for the connection can be reduced so that a work for wiring the flat circuit body 1 can be carried out at a lower cost.
In order to enhance the conducting reliability in a connecting structure between the flat circuit body 1 and the electric connecting terminal 2 shown in FIG. 17, it is important that a contact area or a contact pressure between the piercing portions 7 and 8 penetrating through the conductor 4a (4b) of the flat circuit body 1 and the shear plane of the conductor 4a (4b) should be increased.
With respect to a contact pressure between the conductor 4a (4b) of the flat circuit body 1 and the piercing portions 7 and 8, as a compression stress Fp is greater, the contact pressure is increased. The compression stress Fp is defined by stress due to the contact between inner surfaces 7c and 8c of the base internal portion 7c and 8c of the piercing portions 7 and 8 and the shear plane of the conductor 4a (4b) as shown in FIG. 17 when the tip sides of the piercing portions 7 and 8 penetrating through the flat circuit body 1 are folded and molded in such direction as to approach each other.
However, in the related electric connecting terminal 2, when the tips of the piercing portions 7 and 8 are caused to pierce the flat circuit body 1, the taper surfaces 7b and 8b formed on the external surface side of the tip portions of the piercing portions 7 and 8 undergoes an inward drag T1 as shown in FIG. 18. Therefore, the piercing portions 7 and 8 penetrating through the flat circuit body 1 is easily brought into such a state as to be tilted inwardly.
When folding and molding are to be carried out by the caulking device 9 while the piercing portions 7 and 8 are tilted inwardly, the compression stress FP in a transverse direction which is to be applied to the conductor 4a (4b) present between the piercing portions 7 and 8 by the base internal surfaces 7c and 8c is reduced and it becomes difficult to increase the contact pressure.
More specifically, in the related electric connecting terminal 2, it is hard to maintain a sufficient contact pressure between the conductor 4a (4b) and each of the piercing portions 7 and 8. As shown in an arrow (A) of FIG. 19, when the tip returns by a spring back after the folding and molding, the contact pressure between the base internal surfaces 7c and 8c and the conductor 4a (4b) is reduced. Consequently, there is a possibility that conducting reliability may be deteriorated or a mechanical connecting strength may be reduced.
Moreover, the piercing portions 7 and 8 of the related electric connecting terminal 2 have almost triangular shapes seen from the side by the taper portions 7a and 8a from a base portion to a tip. The cross-sectional areas of the piercing portions 7 and 8 are gradually reduced toward the tip side. For example, therefore, it is also supposed that the area of the contact with the conductor 4a (4b) is decreased so that the conducting reliability is deteriorated when a return is generated in a direction of penetration shown in an arrow (B) of FIG. 19 through the spring back after the repetitive folding and molding.